hr A. 


[Reprinted  from  Biological  Bulletin.  Vo!.  IX.,  No.  6,  November,  1905.] 


TEMPERATURE  AS  A FACTOR  IN  THE  DEVELOP- 
MENT OF  ANTS. 


With  Further  Observations  on  Ants  Deprived  of  Food. 


ADELE  M.  FIELDE. 


Some  recent  experiments  made  by  me  lead  to  the  conclusion 
that  temperature  is  a dominant  factor  in  the  development  of  ants  ; 
that,  other  things  being  equal,  it  determines  the  time  of  the  de- 
posit of  the  eggs,  the  length  of  the  larval  period,  and  the  hour 
of  exit  from  the  cocoon  ; and  that  the  developing  young  of  un- 
like species  of  ants  are  differently  affected  by  the  same  degree  of 
heat.  It  also  appears  probable  that  unlike  species  of  ants  develop 
and  deposit  their  eggs  at  different  temperatures,  fixed  for  each 
species. 

The  greater  activity  of  the  adult  ants  in  higher  temperatures, 
with  the  increased  movement  of  the  anterior  end  of  the  larva 
which  may  be  observed  when  the  temperature  rises,  and  the 
quickening  of  the  pupae  which  occurs  in  the  hottest  days,  are 
doubtless  an  effect  of  the  stimulation  of  metabolism  by  heat. 

Experiment  A. 


My  N.  queen  Campo7iotus  pennsylv aniens  laid  eggs  in  the  first 
week  in  August,  1903,  which  were  kept  in  my  living  room  where 
the  temperature  seldom  rose  above  7 o°  F.  or  210  C.,  and  the 
earliest  ant  to  issue  from  these  eggs  hatched  on  April  25,  1904, 
when  the  temperature  had  risen  to  78°  F.  or  26°  C.  On  July 
14,  1904,  I removed  this  queen  to  a new  nest,  where  she  was  kept 
at  a temperature  that  seldom  rose  above  70°  F.,  and  she  laid  no 
eggs  until  after  I had,  on  November  20,  1904,  removed  her  to  a 
room  wThere  the  usual  temperature  was  from  82°  to  85°  F.,  rarely 
falling  to  70°  F.  and  occasionally  rising  to  90°  F.  On  Decem- 
ber 2 I observed  twenty  eggs,  which  had  increased  to  sixty  on 
December  11.  The  first  larva  appeared  on  December  18.  On 
December  30  all  the  eggs  had  hatched  and  there  were  several 
tens  of  larvae.  The  first  cocoon  was  spun  on  January  8,  and  the 


361 


T 15060 


362 


ADELE  M.  FIELDE. 


first  callow  appeared  on  January  29,  1905.  This  indicates  about 
twenty  days  for  incubation,  a month  for  the  larval  and  twenty 
days  for  the  pupal  period,  all  at  a time  when  the  congeners  of 
this  queen  were  merged  in  winter  repose. 

This  N.  queen  shared  the  labors  of  the  workers  in  the  care  of 
the  young,  which  continued  to  develop  until  the  26th  of  March, 
when  I removed  the  nest  to  a room  having  a fairly  steady  tem- 
perature of  70°  F.  At  this  temperature  the  remaining  cocoons 
failed  to  hatch,  and  the  fifty  larvae  ceased  to  grow.  The  larvae 
did  not  increase  in  size  till  the  last  days  of  the  following  June, 
after  the  temperature  had  risen  to  76°  F.  The  first  cocoon  of 
this  newer  brood  was  spun  August  6,  1905. 

Although  this  queen  had  deposited  eggs  in  March,  1904,  she 
deposited  none  in  March,  1905,  nor  did  she  lay  any  thereafter 
until  July  26,  1905,  when  she  again  deposited  a few  eggs. 
During  the  first  week  in  August,  1905,  the  eggs  were  increased 
to  about  the  same  number  that  she  had  laid  at  the  same  season 
two  years  previously.  Her  failure  to  lay  eggs  in  August,  .1904, 
was  doubtless  due  to  the  agitation  consequent  upon  her  service 
in  several  of  my  experiments  at  about  that  time.  I have  often 
observed  that  psychic  influences  affect  the  deposit  of  eggs  by  ant 
queens.  Her  failure  to  lay  eggs  in  March,  1905,  was  probably 
due  to  exhaustion  consequent  upon  the  work  to  which  she  had 
been  stimulated  by  high  temperature  in  the  previous  December. 

Since  the  food  supply,  the  humidity,  and  the  number  of  workers 
were  factors  whose  variation  was  but  slight  in  the  nest  of  this 
queen,  it  appears  probable  that  the  time  of  the  development  of 
eggs  and  the  growth  of  the  young  was  determined  mainly  by  the 
temperature. 

Experiment  B. 

My  Cremastogaster  lineolata  queen  laid  hundreds  of  eggs  in 
August,  1 904,  and  the  larvae  therefrom  grew  scarcely  at  all  until, 
on  November  20,  1904,  I removed  her  nest  from  a room  where 
the  usual  temperature  had  been  70°  F.  t&  a chamber  where  the 
temperature  was  usually  from  82°  to  85°  F.  Early  in  Decem- 
ber the  larvae  began  to  increase  in  size  and  on  December  22  the 
first  pupa  appeared  among  them.  The  young  continued  to  thrive 
and  fifty-three  pupae  had  been  developed  in  the  nest  before  March 


TEMPERATURE  IN  THE  DEVELOPMENT  OF  ANTS.  363 

26,  1905,  when  I removed  the  nest  to  a room  having  a usual 
temperature  of  70°  F.  No  more  pupae  developed  thereafter 
until  late  in  the  succeeding  summer.  The  larvae  remained  in 
a state  of  arrested  development  from  the  end  of  January  until  the 
end  of  the  following  June,  when,  under  the  influence  of  the  natu- 
ral rise  in  summer  heat,  they  entered  upon  a period  of  renewed 
growth  and  in  August  presented  me  with  ten  more  pupae. 

This  queen  laid  eggs  in  June,  when  the  temperature  rose  to 
750  F.,  and  continued  to  deposit  them  at  various  times  throughout 
the  summer. 

Experiment  C. 

A group  of  thirty  workers,  majors  and  minors,  of  Camponotus 
herculeanus  picins  hatched  between  July  11  and  31,  1904,  were 
kept  at  the  temperature  of  70°  F.  or  22 0 C.  until  November  20, 
when  they  were  removed  to  a chamber  whose  usual  temperature 
was  from  82°  to  85°  F.  or  28°  to  30°  C.  On  March  26,  1905, 
they  were  returned  to  their  place  in  my  living-room,  where  the 
temperature  was  usually  at  70°  F.  They  laid  no  eggs  until 
May  14,  and  then  deposited  about  fifty  before  June  4,  1905, 
apparently  under  the  influence  of  a rise  in  the  temperature  to 
78°  F.  or  250  C. 

The  age  of  these  ants  may,  however,  have  had  influence  on 
the  time  of  egg-laying.  It  would  be  interesting  to  ascertain,  by 
dissections  of  worker-ants,  whether  differences  in  the  degree  of 
development  of  the  ovaries  in  workers  of  the  same  species  is 
correlated  with  difference  of  age  in  the  respective  workers.  It 
may  be  that  the  ovaries  of  many  worker-ants  do  not  develop 
until  some  months,  or  until  the  second  season,  after  hatching. 

Experiment  D. 

A group  of  fifty  workers,  Formica  argentata  hatched  during 
September,  1904,  were  kept  by  me  at  a fairly  steady  temperature 
of  70°  F.,  and  laid  no  eggs  until  after  they  were  removed  to  a 
chamber  having  a usual  temperature  of  from  82°  to  85°  F. 
Their  first  egg  was  deposited  on  January  1,  1905,  and  during  the 
ensuing  week  the  eggs  increased  rapidly  in  number,  so  that  on 
January  8 there  were  more  than  one  hundred.  The  first  larva 
was  observed  on  January  15.  None  of  the  larvae  reached  the 


364 


ADELE  M.  FIELDE. 


pupa-stage,  and  all  these  eggs  and  their  issue  had  disappeared 
before  March  19.  On  March  26  this  nest  was  removed  to  a 
room  having  a temperature  of  yo°  F.,  and  these  ants  ceased  from 
egg-laying  until  the  temperature  again  rose  to  more  than  8o°  F. 
in  the  following  July.  The  young  larvae  from  the  July  eggs 
rapidly  disappeared  in  the  intense  heat  of  July,  1905,  and  only 
five  of  them  spun  cocoons.  It  seems  that  the  development  of 
the  eggs  of  this  species  demands  a high  temperature,  while  the 
development  of  the  larvae  requires  a lower  degree  of  heat. 

Dr.  Irving  A.  Field,  keeping  a nest  of  one  hundred  and  fifty 
worker-ants  of  this  species,  at  Harvard  University,  gives  me  the 
following  account  of  said  nest:  “ The  ants  all  hatched  between 
August  20  and  September  23,  1904.  They  laid  no  eggs  until 
after  November  30,  when  the  nest  was  placed  in  a chamber 
having  a temperature  of  from  75 0 to  85°  F.  Between  Decem- 
ber 30,  1904,  and  January  9,  1905,  about  a hundred  and  fifty 
eggs  were  laid,  all  of  which  were  subsequently  addled  or  else 
were  eaten  by  the  ants.  But  between  June  6 and  13,  1905, 
about  sixty  eggs  were  laid,  and  from  these,  in  natural  summer 
temperature,  many  larvae  safely  passed  to  the  pupa-stage.” 

Experiment  E. 

I had  one  group  of  virgin  workers  of  Stenamma  fulvum  two 
years  old  ; one  group  of  virgin  workers  of  Stenamma  fulvum  one 
year  old  ; and  one  group  of  virgin  workers  of  Camponotus  ameri- 
canus  newly  hatched,  that  deposited  no  eggs  during  Septem- 
ber, October  and  November,  1904,  when  they  were  kept  at  a 
temperature  of  about  70°  F.  But  in  all  three  of  these  groups, 
eggs  that  produced  larvae  were  deposited  between  November  20, 
1904,  and  March  26,  1905,  when  they  were  kept  at  a tempera- 
ture of  from  82°  to  85°  F.  ; and  all  were  again  subjected  to  a 
completely  arrested  development  of  the  young  when  the  tempe- 
rature fell  to  70°  F.  between  the  end  of  March  and  the  middle 
of  June,  1905. 

Groups  of  virgin  workers  of  Formica  Schaufussi  and  of  Formica 
neogagates , housed,  fed,  and  kept  at  the  same  daily  temperature 
as  were  the  above  named  ants,  laid  no  eggs  during  either  the 


TEMPERATURE  IN  THE  DEVELOPMENT  OF  ANTS.  365 

periods  of  low  or  of  high  temperature,  but  deposited  eggs  after 
the  middle  of  June,  1905,  when  the  summer  heat  rose  to  78°  F. 

Other  Experiments. 

Dr.  Field  had  a nest  of  workers  of  Formica  pallide-fulva  fuscata 
in  which  many  eggs  were  deposited  in  March,  1905,  when  kept 
at  a temperature  of  from  75 0 to  85°  F.  and  the  issue  of  these 
eggs  passed  safely  through  the  larval  and  pupal  stages  at  the 
same  temperature.  Dr.  Field  had  also  a nest  of  Camponotus 
pennsylvanicus  workers  who  failed  to  rear  their  larvae  to  pupation 
in  the  summer  of  1904,  but  who,  under  the  influence  of  the  above 
named  high  temperature  brought  three  to  pupation  in  January, 
1905. 

Dr.  W.  M.  Wheeler  writes  to  me  that  Formica  consocians 
workers  in  his  artifical  nests  deposited  many  hundreds  of  eggs,  in 
March,  1905,  in  a room  whose  temperature  never  rose  above  6o° 
F.  or  1 50  C. 

It  appears  that  the  time  of  development  may  be  altered  by 
change  of  the  prevailing  temperature  and  that  an  intervening 
period  of  recuperation  will  be  maintained  in  spite  of  a continued 
temperature-stimulus.  Other  factors  being  equal,  the  develop- 
ment of  the  eggs  within  the  ovaries,  the  deposit  of  the  eggs,  the 
feeding  and  growth  of  the  larvae,  the  pupation  and  the  hatching, 
all  appear  to  be  determined  by  temperature.  The  degree  of  heat 
suiting  the  species  probably  varies  for  the  different  stages  of 
development. 

All  the  ants  involved  in  my  experiments  had  the  same  food- 
supply,  the  same  daily  temperature,  and  similar  housing.  They 
were  abundantly  provided  with  insect-food  and  with  a variety  of 
sweets.  They  always  appeared  to  be  in  excellent  health,  and 
hardly  any  deaths  occurred  in  any  of  the  nests  mentioned.  It  is 
therefore  difficult  to  refer  behavior  so  varied  to  other  cause  than 
the  varying  effects  of  the  same  temperature  on  unlike  species  of 
ants,  or  to  avoid  the  inference  that  in  different  species  the  young 
develop  best  at  different  degrees  of  heat. 

Among  the  ant-young  observed  by  me,  none  has  developed  at 
a temperature  below  70°  F.  ; while  long  exposure  to  a degree  of 
heat  above  90°  F.  manifestly  causes  injury.  Two  minutes  ex- 


366 


ADELE  M.  FIELDE. 


posure  to  a temperature  of  1220  F.  or  50°  C.  will  kill  the  most 
vigorous  adult. 

Further  Observations  on  Ants  Deprived  of  Food. 

Among  the  groups  mentioned  in  my  paper  on  “ Tenacity  of 
Life  in  Ants  ” (in  the  Biological  Bulletin,  Vol.  VII.,  No.  6, 
Nov.,  1904,  p.  300)  were  seven  Formica  subsericea  workers  that 
had  been  deprived  of  food  three  months  and  remained  alive  at 
the  time  of  writing.  These  seven  ants  had  been  picked  up  from 
a roadside  where  they  were  foraging  under  a linden  tree,  on  July 
3,  1904.  They  were  kept  in  a Petri  cell  containing  only  them- 
selves and  a bit  of  sponge  saturated  with  water.  Cell  and  sponge 
were  cleansed  with  alcohol  at  intervals  never  exceeding  four  days, 
until  the  end  of  September,  after  which  time  the  cell  and  sponge 
were  cleansed  only  once  a week.  No  growths  were  at  any  time 
visible  under  a lens  magnifying  ten  diameters. 

On  February  3,  1905,  one  of  these  ants  was  removed  for  dis- 
section, after  an  enforced  fast  of  just  seven  months.  One  died 
on  November  27,  one  on  November  29,  1904;  one  on  February 
17,  one  on  February  19,  one  on  March  14,  and  one  on  March 
28,  1905,  the  latest  survivor  having  lived  nearly  nine  months 
without  food. 

A Camponotus  Americanus  worker,  under  like  conditions,  lived 
without  food  from  July  13,  1904,  to  February  12,  1905,  just 
seven  months. 

Two  sister  queens,  Camponotus  Americanus , one  dealated,  one 
winged,  under  the  same  conditions,  lived  without  food  from  July 
13  to  December  6,  1904,  both  dying  on  the  same  day.  These 
queens  had  been  bred  in  an  artificial  nest,  and  may  have  lacked 
the  stamina  of  untamed  ants. 

After  the  first  of  October,  all  these  fasting  ants  were  kept  at  a 
fairly  steady  temperature  of  70°  F.  or  21°  C. 

Until  the  day  of  death  the  ants  walked  about,  reacted  normally 
to  light  and  heat,  and  gave  no  evidence  of  failure  in  any  of  the 
senses. 

In  spite  of  the  prolonged  fast,  there  was  no  fighting  nor  can- 
nibalism in  any  group  of  these  ants,  and  the  bodies  of  those  that 
had  died  were  always  found  to  be  intact. 


TEMPERATURE  IN  THE  DEVELOPMENT  OF  ANTS.  367 

The  ability  of  ants  to  survive  a submergence  of  several  days  in 
water  explains  their  persistence  in  areas  where  freshets  periodi- 
cally exterminate  all  other  land  insects,  and  their  power  to  live 
for  many  months  without  food  explains  their  occupancy  of  places 
subject  to  long  droughts  that  destroy  their  whole  food-supply. 

Marine  Biological  Laboratory, 

Wood’s  Holl,  Mass.,  September,  1905. 


